1. Mass media is owned by wealthy people, who do not want other people to question how they amassed that wealth, so corruption is not a widely discuted problem. As long as it doesn't touch everyone personally, it will stay this way.
2. Changing it requires organising. That "organising" is typically called government. It's pretty hard to install a whole new government. Reinstalling government in too slow manner will just reinfect newly elected officials with corruption and won't rid of the disease.
3. After changing government, there are still many wealthy people who will try to corrupt new government. Preventing that requires whole new system of governance, but it is not invented yet.
4. Hard to find THE perpetrators. Too many officials and too many corrupters, which do not make big universally regarded as bad moves. They corrupt little-by-little aka boiling the frog. Many wealthy people and officials are not actually corrupted, we just don't know which are.